Electromagnetic wave shielding filter

ABSTRACT

An electromagnetic wave shielding filter  10  comprises a transparent substrate  1 , and a mesh layer  3  containing an electrically conductive layer  2 , formed on the transparent substrate  1  with a transparent adhesive layer  9 . A transparent colored resin layer  4  containing a coloring agent is formed on the mesh layer  3 , with a transparent barrier layer  5  interposed between the two layers. An anticorrosive layer  6  and a blackening layer  7  are formed on the electrically conductive layer  2  in the mesh layer  3 . The transparent colored resin layer  4  also serves as an adhesive layer, and a functional layer  8 , such as an optical filter, a protective sheet, or a display front substrate, is further laminated to the transparent colored resin layer  4.

FIELD OF THE INVENTION

The present invention relates to an electromagnetic wave shieldingfilter having light transmission properties, and, more particularly, toan electromagnetic wave shielding filter that also functions as anoptical filter and is suitable especially for use with such a display asa PDP.

BACKGROUND ART

There have been known electromagnetic wave shielding filters that aremounted on the front of a variety of displays, such as PDPs (plasmadisplay panels) and CRT (cathode ray tube) displays, in order to shieldelectromagnetic waves that the displays generate. The electromagneticwave shielding filters to be used for this purpose are required to havenot only electromagnetic wave shielding properties but also lighttransmission properties. However, this requirement cannot fully besatisfied by an electromagnetic wave shielding filter produced byforming an ITO (indium tin oxide) film on the entire surface of atransparent substrate (see Patent Documents 1 and 2, for example).Accordingly, there has been proposed an electromagnetic wave shieldingfilter comprising metal foil, such as copper foil, laminated to atransparent resin film substrate by an adhesive, etched into a mesh (seePatent Document 3, for example).

Patent Document 1: Japanese Laid-Open Patent Publication No.278800/1989,

Patent Document 2: Japanese Laid-Open Patent Publication No.323101/1993, and

Patent Document 3: Japanese Laid-Open Patent Publication No.210988/2001.

Further, front filters or the like to be mounted on the front ofdisplays are sometimes required to have not only the function ofshielding electromagnetic waves but also other functions such as thefunction of shielding unwanted light that displays radiate (for example,when mounted on PDPs, light with wavelengths around 590 nm produced byneon emission) to compensate for the color tone of displayed images forenhancing color reproducibility, the function of preventing unwantedreflection of extraneous light, and the function of suppressing unwantedradiation of infrared rays from displays to avoid malfunction ofinfrared ray equipment. Furthermore, the front filters are also requiredto be light in weight and small in thickness. Therefore, when anelectromagnetic wave shielding filter has only the function of shieldingelectromagnetic waves, it is often made into a composite filter, forpractical use, by integrally laminating it to a filter having anotherfunction, such as an antireflection filter, a coloring filter, or aninfrared absorption filter (see Patent Documents 2 and 3, for example).

In the case where a coloring filter containing a coloring agent islaminated to an electromagnetic wave shielding filter for the purpose ofshielding unwanted visible light and infrared rays that a display itselfradiates, or unwanted light such as extraneous light (reflection), noproblem has occurred as long as a coloring filter with a transparentsubstrate is simply laminated to a mesh layer in an electromagnetic waveshielding filter by an adhesive such as a pressure-sensitive adhesive,with the transparent substrate of the coloring filter facing to the meshlayer. FIG. 7(A) shows an example of a conventional electromagnetic waveshielding filter 20 having the above-described structure, that is, anelectromagnetic wave shielding composite filter 20 in which a functionallayer 8, such as an optical filter, composed of a transparent substrate8B and a functioning layer 8A formed on the transparent substrate 8B islaminated to a mesh-laminated sheet 21 composed of a transparentsubstrate 1 and a mesh layer 3 laminated to the transparent substrate 1with an adhesive layer 22 containing no coloring agent, with thetransparent substrate 8B of the functional layer 8 facing to the meshlayer 3 of the mesh-laminated sheet 21. The functioning layer 8A is, forexample, a transparent resin layer in which a near infrared absorber hasbeen incorporated so that the layer has the function of absorbing nearinfrared rays, and, in this case, the functional layer 8 serves as anear infrared absorption filter.

In this structure, the functioning layer 8A is isolated from the metalmesh layer 3 by the transparent substrate 8B and the adhesive layer 22.Therefore, even if the functioning layer 8A has the possibility that itmight undergo a change in color when it interacts with the mesh layer,no such interaction actually occurs due to the transparent substrate 8Band the adhesive layer 22.

However, in order to make the electromagnetic wave shielding compositefilter lighter in weight and smaller in thickness, and to decrease thenumber of the constituent layers of the composite filter (which leads todecrease in cost and haze and to improvement in light transmissionproperties), if the adhesive that is applied when the electromagneticwave shielding filter and the functional layer such as theabove-described coloring filter are laminated is colored with a coloringagent so that the adhesive layer can also serve as a coloring filter,another problem has newly occurred. Namely, it was found that anadhesive colored with a coloring agent undergoes a change in color(discolors or fades) with time.

FIG. 7(B) shows an example of a conventional electromagnetic waveshielding filter 20 having the above-described structure, that is, anelectromagnetic wave shielding composite filter 20 in which a functionallayer 8, such as an optical filter, composed of a transparent substrate8B and a functioning layer 8A formed on the transparent substrate 8B islaminated to a mesh-laminated sheet 21 composed of a transparentsubstrate 1 and a mesh layer 3 laminated to the transparent substrate 1with a transparent colored resin layer 4 serving also as an adhesivelayer, made from a transparent resin to which a coloring agent servingas a neon light absorber, for example, has been added so that the resinlayer has the function of cutting neon light, with the transparentsubstrate 8B of the functional layer 8 facing to the mesh layer 3 of themesh-laminated sheet 21. The functioning layer 8A is, for example, alayer of a transparent resin in which a near infrared absorber has beenincorporated so that the layer has the function of absorbing nearinfrared rays, and the functional layer 8 thus functions as a nearinfrared absorption filter. In this case, it was found that theneon-light-cutting properties deteriorate with time, or that unfavorablecoloring (discoloration) occurs.

It was also found that the coloring agent tends to cause colordeterioration especially when a transparent adhesive layer 9 is presentbetween the transparent substrate 1 and the mesh layer 3, or when themesh layer 3 contains a blackening layer 7, as shown in FIG. 7(C).

SUMMARY OF THE INVENTION

An object of the present invention is, therefore, to prevent anelectromagnetic wave shielding filter comprising an electricallyconductive layer in the form of a mesh from undergoing a change in colorwith time even when its constituent resin layer made from an adhesive orthe like has been colored by a coloring agent so that theelectromagnetic wave shielding filter also functions as a coloringfilter.

The present invention is an electromagnetic wave shielding filtercomprising a transparent substrate, a mesh layer in the form of a mesh,containing at least an electrically conductive layer, formed on thetransparent substrate, and a transparent colored resin layer containinga coloring agent, formed on the mesh layer, a transparent barrier layerthat separates the mesh layer and the transparent colored resin layerfrom each other being present between the mesh layer and the transparentcolored resin layer.

When the electromagnetic wave shielding filter has the above-describedstructure, since the transparent barrier layer prevents the transparentcolored resin layer containing the coloring agent and the mesh layercontaining the electrically conductive layer from coming into directcontact, the transparent colored resin layer undergoes no change incolor with time.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains an anticorrosive layer formed at least onone side of the electrically conductive layer.

When the structure of the electromagnetic wave shielding filter is somade, even if the electrically conductive layer is made from a metalthat rusts easily, since it is covered with the anticorrosive layer, itscarcely rusts, and the electromagnetic wave shielding properties lastlong.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains a blackening layer formed at least on oneside of the electrically conductive layer.

By so making the structure of the electromagnetic wave shielding filter,it is possible to prevent the electrically conductive layer face fromcausing unwanted reflection of light such as extraneous light and thusincrease the contrast of an image displayed on a display.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains a blackening layer, the electricallyconductive layer, and an anticorrosive layer that are situated in thisorder, with the blackening layer on the transparent substrate side.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains the electrically conductive layer, ablackening layer, and an anticorrosive layer that are situated in thisorder, with the electrically conductive layer on the transparentsubstrate side.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains a first anticorrosive layer, a blackeninglayer, the electrically conductive layer, a blackening layer, and asecond anticorrosive layer that are situated in this order, with thefirst anticorrosive layer on the transparent substrate side.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains a first anticorrosive layer, theelectrically conductive layer, a blackening layer, and a secondanticorrosive layer that are situated in this order, with the firstanticorrosive layer on the transparent substrate side.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains the electrically conductive layer, and ablackening layer that covers a face (surface) of the electricallyconductive layer on the side opposite to the transparent substrate sideand the side faces (surfaces) of the electrically conductive layer.

The present invention is the electromagnetic wave shielding filter inwhich the transparent colored resin layer functions as an adhesivelayer, and a functional layer is laminated to the transparent coloredresin layer.

When the structure of the electromagnetic wave shielding filter is somade, it is possible to laminate, as the functional layer, the followingarticle to the transparent colored resin layer that functions also as anadhesive layer: a filter other than an electromagnetic wave shieldingfilter, such as an antireflection filter, an antistatic filter, or acoloring filter; a component part of a display itself, such as a displayfront substrate; a protective sheet; or the like.

The present invention is the electromagnetic wave shielding filterfurther comprising a transparent adhesive layer between the transparentsubstrate and the mesh layer.

This structure is an example of the case where the electricallyconductive layer in the mesh layer is made by etching metal foillaminated to the transparent substrate. In this case, since thetransparent barrier layer also covers the transparent adhesive layer,even if the transparent adhesive layer contains a substance thatunfavorably contributes to discoloration, it is possible to preventdiscoloration that is caused by such a substance.

The present invention is an electromagnetic wave shielding filtercomprising a transparent substrate, a transparent adhesive layer madefrom a urethane adhesive, formed on the transparent substrate, a meshlayer in the form of a mesh, containing at least an electricallyconductive layer made from a metal, formed on the transparent adhesivelayer, and a transparent colored resin layer containing a coloring agentand an adhesive, formed on the mesh layer, a transparent barrier layerfor separating the mesh layer and the transparent colored resin layerfrom each other, made from a non-urethane, non-adhesive solid resin,being present between the mesh layer and the transparent colored resinlayer.

The present invention is the electromagnetic wave shielding filter inwhich the mesh layer contains a blackening layer formed, either directlyor through an anticorrosive layer, on one or more faces selected from aface the electrically conductive layer on the transparent substrateside, a face of the electrically conductive layer on the side oppositeto the transparent substrate side, and the side faces of theelectrically conductive layer.

When the structure of the electromagnetic wave shielding filter is somade, even if the materials for and the lamination of theelectromagnetic wave shielding filter inherently cause colordeterioration of the coloring agent, it is possible to prevent, withcertainty, the transparent colored resin layer from undergoing a changein color with time.

Namely, in the case of the above-described structure, the resin used toform the transparent colored resin layer is a semi-fluid,pressure-sensitive adhesive in which a coloring agent can easily move.Moreover, the layer that will come into contact with the coloring agentmoving in the transparent colored resin layer is made from a materialthat reacts with the coloring agent to readily undergo a change incolor. Specifically, the transparent adhesive layer is made from aurethane resin that can react with a variety of coloring agents to causediscoloration, and the mesh layer is made from a metal that chemicallyreacts with the coloring agent or acts as a catalyst for chemicalreactions (or the mesh layer further contains a blackening layer and ananticorrosive layer that may react chemically with the coloring agent oract as catalysts).

Color deterioration of the coloring agent is thus unavoidable, unless aspecial measure is taken. In the present invention, however, thetransparent barrier layer is made from a non-pressure-sensitive-adhesivesolid resin in which a coloring agent cannot easily move, and thetransparent barrier layer itself is also made from a resin selected fromresins other than urethane resins that easily react with a coloringagent to cause discoloration.

For this reason, even when the electromagnetic wave shielding filter hassuch a structure that color deterioration of a coloring agent easilyoccurs, the transparent barrier layer prevents color deterioration ofthe coloring agent with certainty.

(1) According to the present invention, even if the electromagnetic waveshielding filter comprises, as a coloring filter, a transparent coloredresin layer containing a coloring agent, together with a mesh layercontaining an electrically conductive layer made from copper or thelike, it is possible to prevent the transparent colored resin layer fromundergoing a change in color with time. The original performance of thecoloring filter can therefore be maintained for a long period of time;for example, the coloring filter serves to improve the reproducibilityof color of a displayed image and this function lasts long.

(2) Further, when an anticorrosive layer is formed on either of the twosurfaces of the electrically conductive layer, even if a metal thatrusts easily is used to form the electrically conductive layer, thislayer scarcely corrodes, and its electromagnetic wave shieldingproperties, etc. thus last long.

Furthermore, when a blackening layer is formed on either of the twosurfaces of the electrically conductive layer, this blackening layerprevents the electrically conductive layer face from reflecting light,so that the contrast of an image displayed on a display screen isimproved.

(3) Furthermore, by further laminating a functional layer by the use ofthe transparent colored resin layer as an adhesive layer, it is possibleto obtain an electromagnetic wave shielding filter into which thefollowing article has been integrated as the functional layer: a filterother than an electromagnetic wave shielding filter, such as anantireflection filter or an antistatic filter; a component part of adisplay, such as a display front substrate; a protective sheet; or thelike.

(4) Furthermore, in the structure in which a transparent adhesive layeris present on the transparent substrate including the openings in themesh layer, between the transparent substrate and the mesh layer, evenif the transparent adhesive layer contains a substance that unfavorablycontributes to discoloration, it is possible to prevent discolorationthat occurs due to this substance.

(5) Moreover, even when the electromagnetic wave shielding filter hassuch a structure that color deterioration of the coloring agentcontained in the transparent colored resin layer inherently occurs, thatis, the coloring agent can easily move in the transparent colored resinlayer, and, at the same time, that another layer with which the movingcoloring agent comes in contact contains a substance that readily reactswith the coloring agent or acts as a catalyst in the reaction of thecoloring agent, if a urethane adhesive is selected for the transparentadhesive, a metal, for the electrically conductive material for the meshlayer, a pressure-sensitive adhesive, for the resin for the transparentcolored resin layer, and a non-urethane, non-pressure-sensitive-adhesivesolid resin, for the transparent barrier layer, and these materials areused in combination, or if, in addition to the above, the mesh layercontains one of or both of a blackening layer and an anticorrosivelayer, it is possible to effectively prevent color deterioration of thecoloring agent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) to 1(E) are sectional views illustrating some forms ofelectromagnetic wave shielding filters according to the presentinvention,

FIG. 2 is a plane view illustrating a frame part surrounding a meshlayer,

FIGS. 3(A) to 3(C) are sectional views illustrating some other forms ofelectromagnetic wave shielding filters according to the presentinvention,

FIG. 4 is a sectional view illustrating another form of anelectromagnetic wave shielding filter according to the presentinvention,

FIG. 5 is a sectional view illustrating a further form of anelectromagnetic wave shielding filter according to the presentinvention,

FIGS. 6(A) to 6(D) are sectional views showing the lamination of thevarious electromagnetic wave shielding filters produced, and

FIGS. 7(A) to 7(C) are sectional views illustrating some forms ofconventional electromagnetic wave shielding filters.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the present invention will be describedhereinafter with reference to the accompanying drawings.

FIGS. 1(A) to 1(E) are sectional views illustrating some basic forms ofelectromagnetic wave shielding filters according to the presentinvention.

An electromagnetic wave shielding filter 10 shown in FIG. 1(A) is in themost basic form, and comprises a transparent substrate 1, a mesh layer 3in the form of a mesh, containing an electrically conductive layer 2,formed on the transparent substrate 1, and a transparent colored resinlayer 4 containing a coloring agent, formed on the mesh layer 3.

In addition, a transparent barrier layer 5 is present between the meshlayer 3 and the transparent colored resin layer 4, and by thistransparent barrier layer 5, the mesh layer 3 and the transparentcolored resin layer 4 are isolated from each other so that these twolayers do not come in contact with each other.

An electromagnetic wave shielding filter 10 shown in FIG. 1(B) plainlyshows a form that an anticorrosive layer 6 is further formed on eitherof the two surfaces (faces) of the electrically conductive layer 2 (inthe form shown in this figure, only on one surface (face) on the sideopposite to the transparent substrate 1 side) contained in the meshlayer 3 shown in FIG. 1(A).

An electromagnetic wave shielding filter 10 shown in FIG. 1(C) plainlyshows a form that a blackening layer 7 is further formed on either ofthe two surfaces (faces) of the electrically conductive layer 2 (in theform shown in this figure, only on one surface (face) on the transparentsubstrate 1 side) contained in the mesh layer 3 shown in FIG. 1(B).

Further, an electromagnetic wave shielding filter 10 shown in FIG. 1(D)plainly shows a structure that a functional layer 8 is further laminatedto the transparent colored resin layer 4 that has been made to functionalso as an adhesive layer, with the other parts identical to those ofthe structure shown in FIG. 1(C). The functional layer 8 is, forexample, a layer in the form of a sheet, a plate, or a coating film,having any of the functions of various filters such as antireflection(including, in this specification, so-called anti-glaring) filters,infrared absorption filters, and ultraviolet light absorption filters,those of protective films, and those of component parts of displaysthemselves, such as front substrates.

Furthermore, an electromagnetic wave shielding filter 10 shown in FIG.1(E) plainly shows a structure that a transparent adhesive layer 9 ispresent on the entire surface of the transparent substrate 1 includingthe openings in the mesh layer 3, between the transparent substrate 1and the mesh layer 3, the other parts being the same as those of thestructure shown in FIG. 1(C).

The mesh part 3 may be composed of an electrically conductive layer 2and a blackening layer 7 that are situated in this order, with theelectrically conductive layer 2 on the transparent substrate 1 side(FIG. 3(A)). The mesh part 3 may also be composed of an electricallyconductive layer 2, a blackening layer 7, and an anticorrosive layer 6that are situated in the order stated, with the electrically conductivelayer 2 on the transparent substrate 1 side (FIG. 3(B)). The mesh part 3may also be composed of an anticorrosive layer 6, a blackening layer 7,an electrically conductive layer 2, a blackening layer 7, and ananticorrosive layer 6 that are situated in the order stated, with thefirstly mentioned anticorrosive layer 6 on the transparent substrate 1side (FIG. 3(C)).

Further, the mesh part 3 may be composed of an anticorrosive layer 6, ablackening layer 7, an electrically conductive layer 2, and ananticorrosive layer 6 that are situated in this order, with the firstlymentioned anticorrosive layer 6 on the transparent substrate 1 side(FIG. 6(A)).

Furthermore, the mesh part 3 may be composed of an anticorrosive layer6, an electrically conductive layer 2, a blackening layer 7, and ananticorrosive layer 6 that are situated in the order stated, with thefirstly mentioned anticorrosive layer 6 on the transparent substrate 1side (FIG. 6(B)).

Moreover, the mesh part 3 may be composed of an electrically conductivelayer 2, and a blackening layer 7 that covers a face of the electricallyconductive layer 2 on the side opposite to the transparent substrate 1side and side faces of each opening (FIGS. 6(C) and 6(D)).

SUMMARY

The main feature of the electromagnetic wave shielding filter accordingto the present invention is its structure, that is, the electromagneticwave shielding filter of the invention comprises the transparent coloredresin layer containing a coloring agent, and further comprises, betweenthe transparent colored resin layer and the mesh layer, the transparentbarrier layer for preventing the two layers from coming into directcontact. Although any method can be employed to form the mesh layer onthe transparent substrate, one of the typical methods is that, afterlaminating metal foil and a transparent substrate with a transparentadhesive layer, the metal foil is etched to make openings in it forforming a mesh. Preferably, a pressure-sensitive adhesive or the like isused to form the above-described transparent colored resin layer so thatthe layer also serves as an adhesive layer, and to this transparentcolored resin layer is integrally laminated a functional layer so thatthe electromagnetic wave shielding filter performs a function fit forthe use to which the electromagnetic wave shielding filter will be put,where the functional layer is selected from the following optical items:coloring filters other than the coloring filter made of theabove-described transparent colored resin layer, other functionalfilters (e.g., antireflection filters, infrared absorption filters,etc.), protective films, and component parts of displays themselves,such as front substrates.

The electromagnetic wave shielding filter of the present invention willbe described hereinafter; explanation for the respective constituentlayers will be given in due order, beginning from explanation for thetransparent substrate 1.

[Transparent Substrate]

The transparent substrate 1 is a layer for reinforcing the mesh layerthat is poor in mechanical strength. A material having both mechanicalstrength and light transmission properties may, therefore, be selectedand used for the transparent substrate 1, with due consideration for theuse to which the electromagnetic wave shielding filter will be put, alsofor heat resistance, insulating properties, and so forth. Specificexamples of the transparent substrate include resin plates, resin sheets(including resin films, the same shall apply hereinafter), and glassplates.

Examples of transparent resins to be made into resin plates, resinsheets, or the like include polyester resins such as polyethyleneterephthalate, polybutylene terephthalate, polyethylene naphthalate,terephthalic acid-isophthalic acid-ethylene glycol copolymers, andterephthalic acid-cyclohexane dimethanol-ethylene glycol copolymers;polyamide resins such as nylon 6; polyolefin resins such aspolypropylene and polymethyl pentene; acrylic resins such as polybutylmethacrylate and polymethyl methacrylate; styrene resins such aspolystyrene and styrene-acrylonitrile copolymers; cellulose resins suchas triacetyl cellulose; imide resins; and polycarbonate resins.

As for the material for the transparent substrate, the above-enumeratedresins are used for the transparent substrate either singly or as aresin mixture (including a polymer alloy) of two or more resins. As forthe constituent layers of the transparent substrate, the transparentsubstrate may be composed of either a single layer or a laminate of twoor more layers. In the case where a resin sheet is used for thetransparent substrate, an oriented sheet such as a monoaxially orbiaxially oriented sheet is more preferred from the viewpoint ofmechanical strength.

Further, additives such as ultraviolet light absorbers, fillers,plasticizers, and antistatic agents may be incorporated in these resins,as needed.

Glass useful for the glass plates includes silica glass, borosilicateglass, and soda-lime glass, and, more preferably, non-alkali glass thatcontains no alkali components, has a low rate of thermal expansion andhigh dimensional stability, and is excellent in working properties inhigh-temperature heat treatment. A glass substrate can be made to servealso as an electrode substrate that is used for a display frontsubstrate or the like.

The transparent substrate may be made in any thickness fit for the useto which the electromagnetic wave shielding filter will be put. When atransparent resin is used for the transparent substrate, the thicknessof the transparent substrate is usually about 12 to 1000 μm, preferably50 to 700 μm, and more preferably 100 to 500 μm. On the other hand, whena glass plate is used as the transparent substrate, the preferredthickness of the transparent substrate is usually about 1 to 5 mm. Ineither case, a transparent substrate with a thickness smaller than theabove range cannot have sufficiently high mechanical strength, so thatit curls, becomes wavy, or is broken; while a transparent substrate witha thickness greater than the above range has excessively high strength,demands higher cost, and makes it difficult to obtain a thinner product.

A sheet (or film), a plate, or the like of any of the above-describedinorganic and organic materials may be used as the transparentsubstrate. Further, the transparent substrate may be made to serve alsoas a front substrate, one component part of a display body composed of afront substrate, a rear substrate, and others. In the case where theelectromagnetic wave shielding filter is used as a front filter that isplaced on the front of a front substrate, a transparent substrate in theform of a sheet is superior to that in the form of a plate in thinnessand lightness in weight. It is needless to say that resin sheets aresuperior to glass plates also in unbreakableness.

Further, at least in the initial stage of production, such as the stepof forming a mesh layer, it is preferred that the transparent substratebe in the form of a continuous belt-like sheet, because the use of sucha substrate makes it possible to continuously produce theelectromagnetic wave shielding filter and thus to enhance productivity.

Resin sheets are favorable materials for the transparent substrate forthe above-described reasons. Of the resin sheets, sheets of polyesterresins such as polyethylene terephthalate and polyethylene naphthalate,and cellulose resin sheets are preferred from the viewpoint oftransparency, heat resistance, cost, and so on, and polyethyleneterephthalate sheets are most preferred. A transparent substrate havinghigher transparency is more favorable, and the preferred transparency,as expressed by the transmittance for visible light, is 80% or more.

The surface of the transparent substrate made of a resin sheet or thelike may be subjected to conventional adhesion-promoting treatment suchas corona discharge treatment, plasma treatment, ozone treatment, flametreatment, primer treatment, preheating treatment, dust-removingtreatment, vacuum deposition, or alkali treatment, if necessary.

[Mesh Layer: Electrically Conductive Layer]

The electrically conductive layer 2 is a layer for shieldingelectromagnetic waves, and even if this layer itself is not transparent,it can show both electromagnetic wave shielding properties and lighttransmission properties because of the openings made in the layer toform a mesh. The electrically conductive layer 2 is therefore essentialfor the mesh layer 3 in the form of a mesh. Not only the electricallyconductive layer 2 but also an anticorrosive layer 6, a blackening layer7, and so on that will be described later are considered to beconstituent layers of the mesh layer 3 because the latter layers arealso maintained in the form of the same mesh as that of the electricallyconductive layer, the characteristic form of the mesh layer.

The openings in the mesh may be in any shape and are typically in theshape of a regular square. The shape of the openings include trianglessuch as equilateral triangle, squares such as regular square, rectangle,rhombus, and trapezoid, polygons such as hexagon, circles, and ovals.The mesh has multiple openings in any of these shapes. Linear line partshaving usually a uniform width define the openings, and the openings andthe line parts between the openings are uniform in shape and size overthe entire surface. As for the specific size, it is preferred from theviewpoint of opening rate and the non-recognizability of the mesh thatthe width of the lines that define the openings be 25 μm or less,preferably 20 μm or less; and from the viewpoint of light transmissionproperties, it is preferred that the opening size, defined as [distancebetween the lines or line pitch]−[line width], be 150 μm or more,preferably 200 μm or more.

The bias angle (the angle between the line parts of the mesh and theperipheral side of the electromagnetic wave shielding filter) may beproperly selected with consideration for the pixel pitch and theemission properties of a display so that moiré fringes or the like donot easily occur.

Further, it is sufficient to fulfill the purposes that the area having aplurality of the openings (mesh part 3A) be present at least in the areathat is required to have light transmission properties (the area thatwill face to a display screen). It is therefore not necessary that thearea having a plurality of the openings cover the entire surface of theelectromagnetic wave shielding filter. An example of this case is that,as FIG. 2, a plane view, illustrates, the area not participating inimage display, surrounding the rectangular electromagnetic waveshielding filter 10, is made to serve as a frame part 3B in the shape ofa frame, having no openings, and the area inside the frame part, whichwill face to a display screen, is made to serve as a mesh part 3A havinga plurality of the openings. The frame part 3B can be used forgrounding. The frame part 3B is not needed to be present on the entireperipheral area of the electromagnetic wave shielding filter, but may bepresent, for example, only on one side of the electromagnetic waveshielding filter. It is preferred that the frame part be exposed eitherpartly or entirely for easy grounding. In order to entirely or partlyexpose the frame part, the barrier layer, the transparent colored resinlayer, and so on are formed to cover the mesh part 3A only or the meshpart 3A plus a part of the frame part 3B so that the frame part 3B has aportion remaining exposed.

The main feature of the present invention is its structure that the meshlayer and the transparent colored resin layer are isolated from eachother. Although the electrically conductive layer is typically made ofetched metal foil, a mesh layer made from a material other than metalfoil also functions as a barrier. In the present invention, therefore,any material and method can be used to form the electrically conductivelayer, and it is herein possible to employ any of a variety ofelectrically conductive layers for use in conventional electromagneticwave shielding filters having light transmission properties. Forexample, the electrically conductive layer may be one originally formedinto a mesh on a transparent substrate by printing or plating, or oneoriginally formed on the entire surface of a transparent substrate byplating.

In the case where the electrically conductive layer in the form of amesh is made by etching, a metal layer that has been laminated to atransparent substrate is patterned by etching to make openings in themetal layer, thereby making the metal layer into a mesh. To laminate themetal layer to the transparent substrate, metal foil prepared as themetal layer is laminated to the transparent substrate by an adhesive.Alternatively, without using an adhesive, a metal layer may be formed ona transparent substrate by one of or two or more of physical or chemicalmethods such as vacuum deposition, sputtering, and plating. To form theelectrically conductive layer by etching, metal foil alone that is notyet laminated to a transparent substrate may be etched for patterning tomake the metal foil into a mesh. This electrically conductive layer inthe form of a mesh is then laminated to a transparent substrate by anadhesive or the like. Of these electrically conductive layers, anelectrically conductive layer obtained by firstly laminating metal foilto a transparent substrate by an adhesive and then etching the metalfoil into a mesh is desirable. This is because it is easy to handle suchan electrically conductive mesh layer whose mechanical strength is low,and also because the productivity of such an electrically conductivelayer is high.

Although any material can be used for the electrically conductive layeras long as it has electrical conductivity good enough to exhibitelectromagnetic wave shielding properties, a metal layer is generallypreferred because of its high electrical conductivity, and such a methodas vacuum deposition, plating, or metal foil laminating can be employedto form a metal layer, as described above. Examples of materials usefulfor the metal layer or foil include gold, silver, copper, iron, nickel,and chromium. The metal for the metal layer may also be an alloy, andthe metal layer may be composed of either a single layer or multiplelayers. Low-carbon steels such as low-carbon rimmed steels andlow-carbon aluminum killed steels, Ni—Fe alloys, and invar alloys areherein preferred as iron materials. In the case where the metal iscopper, copper or a copper alloy is used. Although both rolled copperfoil and electrolytic copper foil can be used as the copper foil,electrolytic copper foil is preferred from the viewpoint of thinness,uniformity in thickness, adhesion to the blackening layer, and so forth.

The thickness of the electrically conductive layer made of a metal layeris approximately from 1 to 100 μm, and preferably from 5 to 20 μm. Anelectrically conductive layer with a thickness of less than the aboverange has increased electrical resistance, so that it cannotsatisfactorily show electromagnetic wave shielding properties. On theother hand, an electrically conductive layer with a thickness of morethan the above range cannot be made into the desired fine mesh.Consequently, the mesh has a decreased opening rate, which leads todeterioration of light transmission properties, and, a display,disturbed by the side faces of the openings in the mesh, has a decreasedviewing angle.

Further, in the case where the electrically conductive layer is madefrom a metal, especially from a transition metal such as copper or iron,the reaction of the coloring agent contained in the transparent coloredresin layer with the metal of the electrically conductive layer, or thecatalytic action of the metal, tends to cause color deterioration of thecoloring agent, depending on the combination of the coloring agent andthe metal. Therefore, in such a case, the transparent barrier layer ofthe present invention is particularly effective in preventing colordeterioration of the coloring agent.

It is preferred that the metal layer to be made into the electricallyconductive layer has a roughened surface so that it shows increasedadhesion to the adjacent layer such as the transparent adhesive layer.For example, in the case where copper foil is used as the metal layer,the surface of the copper foil is roughened simultaneously with theformation of a blackening layer on the copper foil by blackeningtreatment (the blackening layer has a roughened surface). The roughnessof the roughened surface is preferably about 0.1 to 10 μm, morepreferably 1.5 μm or less, most preferably 0.5 to 1.5 μm, as expressedby the Rz value, a mean value of 10 measurements obtained in accordancewith JIS-B0601 (1994 version). When the metal layer has such surfaceroughness that the Rz value is lower than the above range, the effect ofsurface roughening cannot be fully obtained. On the other hand, when themetal layer has such surface roughness that the Rz value is greater thanthe above range, an adhesive, a resist, or the like tends to causeincorporation of air bubbles when it is applied to the metal layer.

In the case where the anticorrosive layer contains a metal, especially atransition metal (chromium, zinc, etc.), the reaction of this metal withthe coloring agent contained in the transparent colored resin layer, orthe catalytic action of the metal, tends to cause color deterioration ofthe coloring agent, depending on the combination of the metal and thecoloring agent. Therefore, when such an anticorrosive layer is present,the effect of the transparent barrier layer of the present invention canbe particularly anticipated.

[Mesh Layer: Anticorrosive Layer]

The mesh layer 3 may be composed only of the electrically conductivelayer 2. However, since an electrically conductive layer made of a metallayer can corrode in the course of production, or while it is handled,and deteriorate to have impaired electromagnetic wave shieldingproperties, it is preferable to cover the surface of the electricallyconductive layer with an anticorrosive layer 6 if it is necessary toprevent corrosion of the electrically conductive layer. Further, whenthe blackening layer, which will be described later, is easy to rust, itis preferable to cover both the electrically conductive layer and theblackening layer with an anticorrosive layer. One or more necessaryfaces selected from the front surface, the back surface, and the sidefaces of the electrically conductive layer, with consideration forproduction cost, and so on, may be covered with the anticorrosive layer.Therefore, referring to FIG. 3 and some other figures, the anticorrosivelayer may be formed to cover the front surface only (see FIG. 3(B), forexample), the back surface only, both the front surface and the backsurface (see FIG. 3(C), for example), the side faces (on both sides orone side) only, the front surface and the both side faces, the backsurface and the both side faces, or the front surface and the backsurface and the both side faces.

In this specification, the “front surface” means a face, on the sideopposite to the transparent substrate side, of a layer under discussion(the face on the upper side in the figures; in the case of thetransparent substrate, its face on the upper side in the figures); the“back surface” means a face, on the transparent substrate side, of aparticular layer under discussion (the face on the lower side in thefigures; in the case of the transparent substrate, its face on the lowerside in the figures); and the “side face” means a face connecting thefront surface and the back surface (the face stretching vertically inthe figures) (this description applies equally to the electricallyconductive layer, the functional layer, and the other layers). When theelectromagnetic wave shielding filter is mounted on a display or thelike, the filter face to be directed to the observer side is not alwaysits front surface as herein defined, but can be its back surface.

Any material selected from inorganic materials such as metals, organicmaterials such as resins, combination of these materials, and so forthcan be used for the anticorrosive layer as long as it is less apt torust than the electrically conductive layer on which the anticorrosivelayer will be formed. In some cases, by covering also the blackeninglayer with the anticorrosive layer, it is possible to prevent falling ordeformation of particles with which the blackening layer is formed andalso to enhance the blackness of the blackening layer. Therefore, whenmetal foil is used to make the mesh layer, and a blackening layer isformed beforehand on the metal foil present on the transparent substrateby blackening treatment, it is preferable to form, before laminating thetransparent substrate and the metal foil, the anticorrosive layer on theblackening layer for preventing falling and deterioration of theblackening layer.

The anticorrosive layer 6 may be any of conventional ones includinglayers of metals such as chromium, zinc, nickel, tin, and copper, layersof alloys of these metals, and layers of metallic compounds of metallicoxides. A conventional plating process or the like may be used to formthese layers. An example of the anticorrosive layer favorable from theviewpoint of anticorrosion, adhesion, etc. is a chromium compound layerobtained by conducting zinc plating, followed by chromate treatment. Theanticorrosive layer made of such a chromium compound layer is excellentalso in adhesion to a blackening layer made from copper-cobalt alloyparticles and to a transparent adhesive layer (especially, a two-packcurable urethane resin adhesive); these two layers will be describedlater.

In the case where chromium is used to form the anticorrosive layer,chromate (chromic acid salt) treatment or the like may be carried out.The chromate treatment is conducted by bringing a surface to be treatedinto contact with a chromate treatment liquid. This contact can be madeby such a coating method as roll, curtain, squeeze or flow coating (bywhich one side is brought into contact with a chromate treatmentliquid), and it is also possible to bring both sides into contact with achromate treatment liquid by electrostatic spray or dip coating. Thesurface that has been brought into contact with the chromate treatmentliquid is dried without washing it with water. For the chromatetreatment liquid, an aqueous solution containing chromic acid is usuallyused, and, specifically, such treatment liquids as “Alsurf (trademark)1000” (manufactured by Nippon Paint Co., Ltd., Japan), and “PM-284”(manufactured by Nippon Parkerizing Co., Ltd., Japan) are useful.

To conduct zinc plating prior to the chromate treatment is preferredfrom the viewpoint of adhesion and anticorrosion. Further, a siliconcompound such as a silane-coupling agent may be incorporated in theanticorrosive layer in order to increase acid resistance that is neededfor etching or washing with an acid.

The thickness of the anticorrosive layer is usually about 0.001 to 10μm, preferably from 0.01 to 1 μm.

In the case where the anticorrosive layer contains a metal, especially atransition metal (nickel, zinc, etc.), the reaction of the metal withthe coloring agent contained in the transparent colored resin layer, orthe catalytic action of the metal, tends to cause color deterioration ofthe coloring agent, depending on the combination of the metal and thecoloring agent. Therefore, when such an anticorrosive layer is present,the effect of the transparent barrier layer of the present invention canbe particularly anticipated.

[Mesh Layer: Blackening Layer]

The blackening layer 7 can improve the contrast of an image displayed ona display in a bright room. Some blackening layers have roughenedsurfaces and can therefore have increased adhesion to the adjacentlayer, as mentioned before. In order to improve the contrast of an imagedisplayed on a display, it is preferable to form the blackening layer onall of the faces of the mesh layer (the electrically conductive layer,or the electrically conductive layer on which the anticorrosive layerhas been formed) that are seen by a viewer. However, an adequate effectcan be obtained when the blackening layer is formed at least on one faceselected from the front surface, the back surface, and the side faces ofthe mesh layer. Therefore, the blackening layer may be formed to cover,for example, the front surface only (see FIG. 3(A), for example), theback surface only (see FIG. 1(C), for example), both the front surfaceand the back surface (see FIG. 3(C), for example), the side faces (onboth sides or one side) only, the front surface and the both side faces(see FIGS. 6(C) and 6(D), for example), the back surface and the bothside faces, or the front surface and the back surface and the both sidefaces, although the selection of faces to be covered depends on theposition of the electromagnetic wave shielding filter in relation to adisplay.

In any case, any layer selected from conventional blackening layers maybe used as long as it assumes a dark color such as black and meets therequired basic physical properties such as adhesive properties.

Therefore, inorganic materials such as metals, organic materials such asblack-colored resins, and so forth can be used for the blackening layer.For example, when an inorganic material is used, a metallic layer of ametal or alloy, or that of a metallic compound of a metallic oxide orsulfide is formed as the blackening layer. To form a metallic layer, aproper method selected from a variety of conventional methods useful forblackening treatment can be employed. Of these, blackening treatment byplating is preferred from the viewpoint of adhesion, uniformity,easiness, and so on. Materials herein useful for plating include metalssuch as copper, cobalt, nickel, zinc, molybdenum, tin, and chromium, andmetallic compounds. These metals are superior to cadmium or the like inadhesion, blackness, and so forth.

A plating process that is favorably employed to conduct blackeningtreatment to form a blackening layer on an electrically conductive layermade from copper such as copper foil is cathodic electrodepositionplating in which the copper-made electrically conductive layer issubjected to cathodic electrolysis in an electrolyte such as sulfuricacid, copper sulfate, or cobalt sulfate, thereby depositing cationicparticles on the copper foil. When this process is employed, thedeposited cationic particles blacken the electrically conductive layer,and, at the same time, roughen the surface of this layer. Copper orcopper alloy particles can be used herein as the cationic particles.Copper-cobalt alloy particles are preferred for the copper alloyparticles, and their mean particle diameter is preferably from 0.1 to 1μm. A blackening layer made of a copper-cobalt alloy particle layer canbe obtained by depositing copper-cobalt alloy particles. Cathodicelectrodeposition is convenient to deposit uniformly sized particleswith a mean particle diameter of 0.1 to 1 μm. When the mean particlediameter is greater than the above range, the deposited particles havedecreased denseness and blackness and are poor in uniformity, and thefalling of the particles (the falling of the powdery coating) easilyoccurs. Also when the mean particle diameter is smaller than theabove-described range, the deposited particles have decreased blackness.If treated at high current density in the cathodic electrodeposition,the surface becomes cathodic and generates reducing hydrogen to getactivated, so that significantly improved adhesion can be obtainedbetween the copper face and the cationic particles.

Further, black chromium, black nickel, nickel alloys, and the like arealso preferred for the blackening layer, and the nickel alloys includenickel-zinc alloys, nickel-tin alloys, and nickel-tin-copper alloys. Inparticular, nickel alloys are excellent in blackness and electricalconductivity, and, moreover, can form anticorrosive blackening layers(serving as both the blackening layer and the anticorrosive layer).Therefore, if a nickel alloy is used to form the blackening layer, theanticorrosive layer may be omitted. In addition, since the particlesforming the blackening layer are usually needlelike, they are readilydeformed by external forces and undergo a change in appearance. However,nickel alloy particles are not so easily deformed, so that theblackening layer made from nickel alloy particles is advantageous inthat it scarcely undergoes a change in appearance in the subsequentprocessing steps. A conventional electroplating or electroless platingprocess may be used to deposit a nickel alloy to form the blackeninglayer. The deposition of a nickel alloy may be effected after conductingnickel plating.

When the blackening layer is made from a metal such as a metalliccompound or an alloy, especially when it is made from a transition metal(nickel, etc.), the reaction between the metal in the blackening layerand the coloring agent in the transparent colored resin layer, or thecatalytic action of the metal, tends to cause color deterioration of thecoloring agent, depending on the combination of the metal and thecoloring agent. Therefore, when a blackening layer containing a metal ispresent, the effect of the transparent barrier layer of the presentinvention can be particularly anticipated.

[Transparent Adhesive Layer]

The transparent adhesive layer 9 is for laminating and fixing the meshlayer 3 to the transparent substrate 1. This layer can be omitted,depending on the manner in which the mesh layer is formed. An example ofthe case where the transparent adhesive layer 9 is needed is that metalfoil to be made into the electrically conductive layer in the mesh layeris laminated and fixed to the transparent substrate by an adhesive. Inthis case, it is necessary to use a transparent adhesive for laminatingthe metal foil to the transparent substrate so that the adhesive that isseen through the openings in the electrically conductive layer does notimpair the light transmission properties. In particular, in the casewhere, after laminating metal foil to a transparent substrate, the metalfoil is etched to make openings in it to form a mesh, the adhesive isrequired to have transparency because it is exposed at each opening. Forthis reason, it is preferred that the electrically conductive layer 2made of the metal foil and the transparent substrate be laminated with atransparent adhesive layer made from a transparent adhesive.

Any proper laminating method selected from conventional ones may be usedto laminate the metal foil and the transparent substrate. Of theconventional laminating methods, dry laminating is a common method whena resin sheet, a typical material, is used for the transparentsubstrate.

Any proper transparent adhesive selected from conventional ones can beused as the transparent adhesive to form the transparent adhesive layer.Examples of transparent adhesives herein useful include urethaneadhesives, acrylic adhesives, epoxy adhesives, and rubber adhesives. Ofthese, urethane adhesives are preferred from the viewpoint of adhesivestrength, and so on. Such urethane adhesives include two-pack curableurethane resin adhesives, which use two-pack curable urethane resinscontaining various hydroxyl-group-containing compounds and variouspolyisocyanate compounds.

Examples of hydroxyl-group-containing compounds include polyols such asacrylic polyols, polyester polyols, polyether polyols, and polycarbonatepolyols. Examples of polyisocyanate compounds include aromaticisocyanates such as tolylene diisocyanate, xylylene diisocyanate,naphthalene diisocyanate, and diphenylmethane diisocyanate, aliphatic oralicyclic isocyanates such as hexamethylene diisocyanate, hydrogen-addedtolylene diisocyanate, and isophorone diisocyanate, and polymers oraddition products of these isocyanates.

In the case where the transparent adhesive layer is present, especiallywhen a urethane adhesive is used, the color of the coloring agent tendsto change depending upon the combination of the adhesive and thecoloring agent. The reason for this is possibly as follows: a metallicion contained in an etchant that is used for etching the electricallyconductive layer to make it into a mesh, such as ferric iron ioncontained in an aqueous ferric chloride solution, penetrates thoseportions of the transparent adhesive layer that are exposed at theopenings, and causes color deterioration of the coloring agent.Especially when a urethane adhesive is used, color deterioration of thecoloring agent is caused by the reaction of urethane bond with thecoloring agent. Therefore, when the transparent adhesive layer ispresent, especially when a urethane adhesive is used, the effect of thetransparent barrier layer of the present invention can be particularlyanticipated.

The transparent adhesive layer may be formed in the following manner: atransparent adhesive is applied to either of or both of metal foil(preferably, metal foil before being made into a mesh) and a transparentsubstrate by a conventional method of application, and the two membersare then laminated to each other. The method of application includescoating methods such as roll, comma, or gravure coating, and printingmethods such as screen or gravure printing. Although the transparentadhesive layer may be formed in any thickness (when dried), thethickness is usually from 0.1 to 20 μm; and a thickness of 1 to 10 μm ismore preferred from the viewpoint of adhesive strength, cost, workingproperties, and so forth.

[Transparent Colored Resin Layer]

The transparent colored resin layer 4 is a layer for making theelectromagnetic wave shielding filter also function as an opticalfilter, and it is a resin layer made from a transparent resin matrix inwhich a coloring agent has been incorporated. To form the transparentcolored resin layer, a resin composition prepared by adding the desiredcoloring agent to a binder consisting of a transparent resin or the likemay be applied by a conventional method of forming a layer, such ascoating. To the binder, a variety of additives useful for coatingliquids or ink, such as solvents and dispersion stabilizers, may beoptionally added, and, moreover, photostabilizers such as ultravioletlight absorbers may also be added, if necessary. Further, it is alsopreferred that the transparent colored resin layer be made to serve alsoas an adhesive layer so that it can be used to integrate a functionallayer, such as another optical filter or an optical article, into theelectromagnetic wave shielding filter.

By the word “colored” is herein meant that a layer is made to absorblight with wavelengths at least in a part of the wave range coveringfrom the ultraviolet region to the visible light range and to theinfrared region. For example, a resin layer in which a coloring agentthat absorbs light in the visible light range has been incorporatedappears literally pigmented (to a color including achromatic color suchas dark gray). However, when a coloring agent that absorbs light in theultraviolet or infrared region only and absorbs no or substantially nolight in the visible light range is incorporated in a resin layer, thehuman eyes cannot recognize the resin layer as being colored. Even sucha resin layer is also referred to as a “colored”-resin layer in thisspecification.

A coloring agent fit for the purpose of the electromagnetic waveshielding filter serving as an optical filter is used as theabove-described coloring agent. Therefore, when the purpose of theoptical filter is to improve color reproducibility by suppressing theemission of neon from a PDP, it is proper to use a coloring agent thatgreatly absorbs light of approximately 590 nm in the neon emissionspectrum. For preventing malfunction of infrared ray equipment, it isproper to use a coloring agent that has absorption in the infrared ornear infrared region. When such a coloring agent has absorption also inthe visible light range, but the absorption is non-uniform, the layer isunfavorably colored, and the white balance of an image displayed cannotbe maintained. For avoiding this phenomenon, it is proper to co-use acoloring agent that has absorption in the other part of the visiblelight range, thereby making the light absorption neutral (achromatic)over the entire visible light range.

Although conventional inorganic or organic coloring agents can be usedfor the above-described coloring agent, coloring agents that scarcelyincrease haze are preferred from the viewpoint of light transmissionproperties. From this point of view, dyes are generally more favorablefor the coloring agent than pigments. However, some pigments areexcellent in light transmission properties (light transmittance), and,moreover, they are generally superior to dyes in weathering resistance,so that a properly selected pigment is herein useful. Further, it is amatter of course that two or more types of coloring agents, includingpigments and dyes, may be used in combination. Furthermore, thetransparent colored resin layer may be composed of two or more layers,and, in the case of a multi-layered transparent colored resin layer, thetype of the coloring agent, the amount of the coloring agent to beco-used, the amount of the coloring agent(s) to be incorporated, and soon may be varied from layer to layer. The amount of the coloringagent(s) may be properly decided by the required properties, thethickness of the transparent colored resin layer, and so forth, and itis from 0.001 to 50% by weight of the total weight of the resin materialcontained in the transparent colored resin layer, for example.

Of the above-described coloring agents, those coloring agents thatabsorb infrared rays, especially near infrared rays (near infraredabsorbers, NIR absorbers), specifically include phthalocyanine dyes andnaphthalocyanine dyes (see Japanese Laid-Open Patent Publications No.120186/1996 and No. 279125/1997, etc.), anthraquinone dyes (see JapaneseLaid-Open Patent Publications No. 43605/1985, No. 115958/1986, No.291651/1986, No. 132963/1987, and No. 172458/1989, etc.), amminium saltdyes (see Japanese Laid-Open Patent Publications No. 236131/1985 and No.174403/1992, etc.), dithiol metal complex pigments (see JapaneseLaid-Open Patent Publications No. 21458/1982, No. 32003/1986, and No.187302/1987, Japanese Patent Publication No. 32003/1986, and JapaneseLaid-Open Patent Publication No. 32003/1986, etc.), and diimmonium saltdyes (see Japanese Laid-Open Patent Publications No. 178808/1993, No.295967/1993, and No. 310031/1997, etc.).

A coloring agent that absorbs light produced by neon emission (neonlight absorber, Ne light absorber) is used to shield light withwavelengths of approximately 590 nm produced by neon emission from aPDP, in order to compensate for the color tone of an image to improvecolor reproducibility. Such a coloring agent is one that has the maximumabsorption in the vicinity of 590 nm, and typical examples of coloringagents of this type include polymethine coloring agents (dyes) (seeJapanese Laid-Open Patent Publication No. 53799/2004), cyanine dyes,xanthene dyes, azomethine dyes, and porphine dyes.

A coloring agent selected from a variety of conventional coloring agentsincluding pigments and dyes, such as azo pigments, phthalocyanine dyes,and anthraquinone dyes, may be used as the coloring agent that absorbslight in the visible light range.

Thus, the coloring agent is properly used depending on the purpose forwhich it is employed, and coloring agents that serve as near infraredabsorbers or neon light absorbers are of great importance when theelectromagnetic wave shielding filter is used for a display, and comeunder the group of coloring agents for which the present invention iseffective.

The causes of the phenomenon that the transparent colored resin layerundergoes a change in color with time when this layer is in directcontact with the mesh layer are not yet clear. It is, however, possibleto avoid this phenomenon by placing a resin layer between the twolayers, so that one of the causes is probably that the metal or metallicion (the metallic ion that has been present in an etchant and haspenetrated in the electrically conductive layer, the blackening layer,the anticorrosive layer, or the transparent adhesive layer), a non-resincomponent, acts on and affects the absorption spectrum of the coloringagent contained in the transparent colored resin layer. Further, whenthe coloring agent is a compound having a counter ion, the metal ormetallic ion is considered to have a greater influence on the counterion.

Another possible cause is assumed to be as follows: when the transparentadhesive layer is made from a urethane adhesive, urethane bond in theadhesive reacts with a certain type of coloring agents, such asdiimmonium dyes and phthalocyanine dyes, to cause a change in thetransmission spectrum of the coloring agent.

For the transparent colored resin layer can be used any transparentresin as long as it is properly selected from conventional ones withconsideration for, for example, the adhesion to the adjacent layers suchas the transparent barrier layer and the functional layer. For example,thermoplastic resins, thermosetting resins, andionizing-radiation-curing resins are useful for the transparent coloredresin layer. Examples of thermoplastic resins include acrylic resins,polyester resins, thermoplastic urethane resins, and vinyl acetateresins; examples of thermosetting resins include urethane resins, epoxyresins, and curable acrylic resins; and examples ofionizing-radiation-curing resins include acrylate resins that cure inultraviolet light or electron beams (such as those resins that will beenumerated later as materials useful for the transparent barrier layer).

It is also favorable to make the transparent colored resin layer alsoserve as an adhesive layer so that it is convenient to furtherintegrally laminate a functional layer, such as an optical filter, toit. By integrally laminating a functional layer to the transparentcolored resin layer serving also as an adhesive layer, it is possible tomake the number of the constituent layers smaller (no additionaladhesive layer being needed), which leads to decrease in cost and haze,improvement in light transmission properties, and reduction in weightand thickness. When the transparent colored resin layer is made to servealso as an adhesive layer useful in laminating the functional layer, notonly the above-described resins but also resins that becomepressure-sensitive adhesives can be used to form the transparent coloredresin layer. Namely, the adhesiveness of the adhesive layer of thepresent invention encompasses tackiness. The “pressure-sensitiveadhesive” herein means an agent that enables a layer to adhere toanother object only with the tackiness of the surface of the layer whena proper pressure (such a pressure as is exerted lightly by the hand) issimply exerted to the layer. In order for a pressure-sensitive adhesiveto reveal its tackiness, physical actions or energy such as heating,moistening, or irradiation, or chemical reactions such as polymerizationreaction are not needed. A pressure-sensitive adhesive is not fullysolidified even after a diluent has been evaporated, and remains in asemi-fluid state. Therefore, conventional adhesives, as well asconventional pressure-sensitive adhesives, can be used as the resin forthe transparent colored resin layer. Examples of resins that becomepressure-sensitive adhesives include acrylic resins, silicone resins,and rubber resins.

In the case where the binder (resin component) of the transparentcolored resin layer is a pressure-sensitive adhesive, the binder resinremains in a semi-fluid state even after a functional layer has beenlaminated, so that the coloring agent added to the binder resin moveswith time in the transparent colored resin layer. This tendency issignificant especially when the coloring agent is an organic materialhaving a relatively low molecular weight. In this case, therefore, aprobability that the coloring agent will react with the mesh layer orthe transparent adhesive layer becomes high, and color deterioration ofthe coloring agent thus easily occurs. For this reason, when the binderof the transparent colored resin layer is a pressure-sensitive adhesive,the transparent barrier layer of the present invention acts effectively.

In the case where the transparent colored resin layer is not made toserve also as an adhesive layer useful in laminating a functional layer,it can be formed, by a conventional method of forming a layer, such ascoating, on the mesh-layer-side surface of the mesh-layer-laminatedtransparent substrate. On the other hand, when the transparent coloredresin layer is made to serve also as an adhesive layer useful inlaminating a functional layer, the following method may also beemployed: a transparent colored resin layer is formed, by a conventionalmethod of forming a layer, such as coating, on the surface of afunctional layer preformed as a substantial being such as a sheet, notyet laminated to a mesh layer; the functional layer to which thetransparent colored resin layer has been laminated is laminatedintegrally to a mesh layer, with the transparent colored resin layerfacing to the mesh layer, by exerting a pressure on the mesh layer witha pressure roll or the like. A specific example of this method is thefollowing method of laminating (forming) layers: a pressure-sensitiveadhesive for forming the transparent colored resin layer is applied to aresin sheet useful for an optical filter such as an antireflectionfilter, or to a resin sheet useful for surface protection, therebyobtaining a pressure-sensitive-adhesive-coated resin sheet; this resinsheet is laminated, by making use of the pressure-sensitive adhesive, toa mesh-laminated sheet obtained by forming a mesh layer on a transparentsubstrate. A conventional separator or the like may be optionallyplaced, for protection, on the tacky face of thepressure-sensitive-adhesive-coated resin sheet. For example, a resinsheet such as a biaxially oriented polyethylene terephthalate film whosesurface has been treated with silicone or the like to be releasable isuseful for the separator.

To form beforehand the transparent colored resin layer on the functionallayer is also convenient to laminate the transparent colored resin layerto the mesh layer in such a manner that the mesh layer includes a framepart useful for grounding, and that the frame part is not covered withthe transparent colored resin layer to remain exposed. The followingmanner, for example, can make it easy to integrally laminate thetransparent colored resin layer and the functional layer to the meshlayer, with the frame part of the mesh layer exposed: a transparentcolored resin layer is continuously formed on a continuous belt-likesheet for the functional layer; this continuous belt-like sheet is cutinto sheets, and each sheet is properly positioned on and laminated to amesh-laminated sheet obtained by laminating a mesh layer to atransparent substrate. In this case, the mesh-laminated sheet may be inthe form of either a continuous belt-like sheet or a cut sheet.

A proper coating method, such as roll, comma, or gravure coating may beemployed to form the transparent colored resin layer. Alternatively,there may also be employed a printing method, such as screen or gravureprinting, by which a transparent colored resin layer in any non-solidpattern can be formed with ease.

Although the thickness of the transparent colored resin layer may beproperly decided with consideration for the amount of the coloring agentto be added, the desired intensity of light absorption, the adhesiveproperties of the transparent colored resin layer that also serves as anadhesive or pressure-sensitive adhesive layer, uniformity in thickness,easiness of production, and so forth, it is approximately 0.1 to 30 μm,for example. The uniformity in thickness brings about uniformity incoloring. Even if the transparent barrier layer has a roughened surface,the purpose is fulfilled as long as the mean thickness of thetransparent colored resin layer on the mesh part of the mesh layer isuniformly maintained over the entire surface of the electromagnetic waveshielding filter, and the thickness of the transparent colored resinlayer at the openings and that at the non-opening portions may bedifferent from each other.

[Transparent Barrier Layer]

The transparent barrier layer 5, existing between the transparentcolored resin layer 4 and the mesh layer 3, is a layer for preventingthe two layers from coming into contact. Any layer may be used for thetransparent barrier layer as long as it can prevent the transparentcolored resin layer and the mesh layer from coming into direct contactwith each other. However, a layer formed by coating or the like is morefavorable than a layer formed by a physical film-forming method such asvacuum deposition because the former layer can be obtained more easilyand is also advantageous from the viewpoint of cost. In this regard, atransparent resin layer made from a transparent resin is suitable forthe transparent barrier layer. Any of various methods of application,such as a coating (post polymerization) method using a solution, adispersion, or a resinous material (a composition containing a monomer,a prepolymer, etc.) liquid, or extrusion coating using a melted resin,may be employed to form a transparent resin layer useful for thetransparent barrier layer. Examples of coating methods herein usefulinclude roll coating, comma coating, gravure coating, curtain coating,squeeze coating, flow coating, electrostatic spraying, and dip coating.It is also possible to employ a printing method, such as screen orgravure printing, by which a transparent resin layer can be formed inany non-solid pattern.

The reason why the barrier layer is made transparent is as follows: whenthe barrier layer is formed by coating or the like on the mesh layerpresent on the transparent substrate, the openings in the mesh layer arealso covered with the barrier layer, unless a special measure is taken;the barrier layer should, therefore, be made transparent so that lighttransmission properties do not deteriorate due to the (transparent)barrier layer formed in the openings. For this reason, if the barrierlayer can be formed or has been formed only on the portions excludingthe openings, it is not always needed to be transparent and may besimply a “barrier layer”. Practically, however, since it is easier toform the barrier layer also in the openings, the barrier layer is formedas a transparent layer. Namely, the transparent barrier layer is a layerthat may be formed also in the openings in the mesh layer. Further, inthe embodiment that the transparent adhesive layer is present on thoseportions of the transparent substrate that correspond to the openings inthe mesh layer, even if the transparent adhesive layer containssubstances such as impurities that undesirably contribute todiscoloration, the transparent barrier layer effectively preventsdiscoloration of the transparent colored resin layer with time that isaffected by such a transparent adhesive layer.

Any resin can be used as the above-described transparent resin as longas it is transparent and can prevent the coloring agent from migratingtoward and coming into contact with the mesh layer and the transparentadhesive layer to cause reaction. In the case where the transparentbarrier layer is formed so that it comes into contact with both the meshlayer and the transparent adhesive layer, a proper transparent resin maybe selected from conventional ones with consideration for the adhesionto the transparent adhesive layer, and so on. Examples of transparentresins herein useful include thermoplastic resins, thermosetting resins,and ionizing-radiation-curing resins. The thermoplastic resins includeacrylic resins, vinyl acetate resins, and thermoplastic urethane resins;and the thermosetting resins include urethane resins, epoxy resins, andcurable acrylic resins. It is preferred that these resins be ofnon-pressure-sensitive adhesive type. Further, it is preferable toselect a transparent resin that can form a solid, non-fluid, transparentbarrier layer. By using such a transparent resin, it is possible toprevent, with certainty, the coloring agent that is contained in thetransparent colored resin layer and that moves in and passes through thetransparent barrier layer to be the cause of discoloration, from cominginto contact with a constituent layer of the mesh layer (theelectrically conductive layer, the blackening layer, or theanticorrosive layer), or with the transparent adhesive layer.

Of these resins, ionizing-radiation-curing resins are preferred becausethey cure in ionizing radiation into a non-sticky, solid state withgreater certainty. Further, ionizing-radiation-curing resins areadvantageous also in that, since they can be applied without using anysolvent, the solvent-evaporating step can be omitted, which leads tohigher productivity. Furthermore, ionizing-radiation-curing resins arepreferred also for the following reason: even when a solvent is added toan ionizing-radiation-curing resin, a small amount of the solventsuffices for the purpose; moreover, since an ionizing-radiation-curingresin can be applied by using no or almost no solvent, it is possible toprevent great volume shrinkage that usually occurs when evaporating asolvent for forming a coating film; and depressions that are thereflections of the openings in the mesh layer formed on the transparentsubstrate are completely filled with the ionizing-radiation-curingresin, which makes it easy to smoothen the surface of the transparentbarrier layer. When smoothness is obtained in this manner, the thicknessof the transparent colored resin layer that is laminated to thetransparent barrier layer is easily made uniform over the entire surfaceof the mesh layer including the openings and the non-opening portions(line parts). Consequently, uniformity in coloring can be easilyattained. In the case where a functional layer, such as another filteror a component part of a display itself, is further laminated to thetransparent colored resin layer by an adhesive or the like, theabove-described smoothening is also effective in preventing the adhesiveor the like from incorporating air bubbles, which occurs when anadherend surface has irregularities.

The ionizing-radiation-curing resins are compositions that causepolymerization or crosslinking to cure when exposed to ionizingradiation that is typically ultraviolet light or an electron beam, andit is herein preferable to use a composition containing a prepolymer(including a so-called oligomer) and/or a monomer. Either a singleprepolymer or monomer, or a mixture of two or more prepolymers ormonomers is used.

Specifically, the above-described prepolymer or monomer is a compoundhaving, in its molecule, a radically polymerizable unsaturated groupsuch as (meth)acryloyl or (meth)acryloyloxy group, a cationicallypolymerizable functional group such as epoxy group, or the like. Theabove-described prepolymer also includes polyene/thiol prepolymers thatare combinations of polyenes and polythiols. (Meth)acryloyl group hereinmeans acryloyl group or methacryloyl group. Similarly, (meth)acrylatethat will be described hereinafter means acrylate or methacrylate.Acrylate compounds and methacrylate compounds are also collectivelyreferred to simply as acrylate (compounds).

Examples of prepolymers having radically polymerizable unsaturatedgroups include polyester (meth)acrylate, urethane (meth)acrylate, epoxy(meth)acrylate, melamine (meth)acrylate, and triazine (meth)acrylate.The molecular weight of these prepolymers useful herein is usually about250 to 100,000.

Examples of monomers having radically polymerizable unsaturated groupsinclude monofunctional monomers such as methyl (meth)acrylate,2-ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate,carboxypolycaprolactam (meth)acrylate, and (meth)acrylamide.

Examples of polyfunctional monomers include difunctional monomers suchas 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,propylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate,and pentaerythritol di(meth)acrylate monostearate; trifunctionalmonomers such as pentaerythritol tri(meth)acrylate, trimethylol propanetri(meth)acrylate, and trimethylol propane ethylene oxidetri(meth)acrylate; and polyfunctional monomers having five or morefunctional groups, such as pentaerythritol tetra(meth)acrylate,dipentaerythritol tetra(meth)acrylate, dipentaerythritolpenta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

Examples of prepolymers having cationically polymerizable functionalgroups include epoxy resin prepolymers such as bisphenol epoxy resinprepolymers and epoxy-novolak resin prepolymers, and vinyl ether resinprepolymers such as aliphatic vinyl ether prepolymers and aromatic vinylether prepolymers.

Examples of thiols include polythiols such as trimethylol propanetrithioglycolate and pentaerythritol tetrathioglycolate. Examples ofpolyenes include polyurethanes obtained from diols and diisocyanates,having allyl alcohol added to their each end.

In the case where ultraviolet light or an electron beam is used to curethe above-described ionizing-radiation-curing resin, aphotopolymerization initiator is further added to the resin beforehand.Examples of photopolymerization initiators suitable forionizing-radiation-curing resins having radically polymerizableunsaturated groups include acetophenones, bonezophenones, ketals,anthraquinones, thioxanethones, azo compounds, peroxides,2,3-dialkyldione compounds, disulfide compounds, thiuram compounds, andfluoroamine compounds. Examples of photopolymerization initiatorssuitable for prepolymers having cationically polymerizable functionalgroups include aromatic sulfonium salts, aromatic diazonium salts,aromatic iodonium salts, and metallocene compounds. Thesephotopolymerization initiators are used singly, or two or more of thesephotopolymerization initiators are used in combination.

Specific examples of the above-described photopolymerization initiatorssuitable for resins having radically polymerizable unsaturated groupsinclude 1-hydroxy-cyclohexyl-phenyl-ketone [trade name “Irgacure(trademark) 184” manufactured by Ciba Specialty Chemicals K.K., Japan],2-methyl-1[4-(methylthio)phenyl]-2-morpholino-propan-1-one [trade name“Irgacure (trademark) 907” manufactured by Ciba Specialty ChemicalsK.K., Japan], benzyl dimethyl ketone,1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one,2-hydroxy-2-methyl-1-phenylpropan-1-one,1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, and benzophenone.

Electromagnetic waves or charged particles having energy high enough tocause the curing reaction of molecules of ionizing-radiation-curingresin (composition) are used as the ionizing radiation. Althoughultraviolet light or an electron beam is usually used as the ionizingradiation, other ionizing radiation such as visible light, X-rays, orion lines may also be used. Examples of ultraviolet light sourcesinclude extra-high-pressure mercury vapor lamps, high-pressure mercuryvapor lamps, low-pressure mercury vapor lamps, carbon arc lamps, blacklight lamps, and metal halide lamps. The wavelength of ultraviolet lightfor use herein is usually about 190 to 380 nm, and the preferred amountof ultraviolet light to be applied is approximately from 50 to 1000mJ/cm². Examples of electron beam sources include a variety of electronbeam accelerators such as Cockcroft-Walton accelerator, Van de Graaffaccelerator, resonance-transformer-type accelerators,insulation-core-transformer-type accelerators, linear accelerators,dynamitron accelerators, and high-frequency accelerators. The preferredenergy of an electron beam to be applied is from 70 to 1000 keV,preferably from 100 to 300 keV, and such an electron beam is usuallyapplied in an amount of approximately 5 to 300 kGy.

In FIGS. 1, 3 and 5, the transparent barrier layer 5 is illustrated ashaving a continuous, flat surface (the boundary front surface on theupper side in each figure) covering the openings and the non-openingportions. However, this surface is not necessarily flat. For example, asconceptually illustrated in FIG. 4 that is a sectional view of anelectromagnetic wave shielding filter 10, this front surface of thetransparent barrier layer 5 may also be rough. The roughened surfaceshown in FIG. 4 has depressions at portions that correspond to theopenings in the mesh layer. The purpose of the transparent barrier layeris to prevent the mesh layer and the transparent colored resin layerfrom coming into contact with each other, so that even such a roughenedsurface as is shown in FIG. 4 can fully meet this purpose. In FIGS. 1, 3and 5, and some other figures excluding FIG. 4, showing anelectromagnetic wave shielding filter of the present invention, thefront surface of the transparent barrier layer is depicted as a flatsurface. However, these figures are merely conceptual, and this frontsurface may be either flat (as shown in the figures) or rough. The flatfront surface shown in the figures encompasses both a flat front surfaceand a roughened surface. The flat front surface may be or may not be amirror surface. The flat front surface is a surface having noirregularities that correspond at least to the distribution, in thedirection in which the front surface stretches, of thickness of the meshlayer (such irregularities that those portions of the surface thatcorrespond to the openings form depressions and that the other portionsof the surface that correspond to the non-opening portions formprotrusions), or a surface that has irregularities of the above type orof other type but has flatness to such a degree that air bubbles arescarcely incorporated when the transparent colored resin layer is formedon this surface by coating or the like, and that distortion of an imagedisplayed on a display or scattering of light that makes the image hazydoes not occur. Thus, the flat surface includes a slightly roughenedsurface that is a reflection of the mesh layer, and, at the same time,is a mirror or matte face, and a surface that has neither smallirregularities nor sharp irregularities at portions that correspond tothe openings in the mesh layer and is flat but is a matte face havingfine irregularities. Namely, a flat surface and a mirror surface areconceptually different from each other; whether a surface is a mirrorsurface or a non-mirror surface is determined by irregularities that arefiner than those by which a surface is determined whether it is flat ornon-flat.

To make the front surface of the transparent resin barrier layer matteis advantageous in that a pyramid phenomenon (when an intermediate sheetof an electromagnetic wave shielding filter, which includes atransparent barrier layer formed on a sheet transparent substrate sheet,is wound up into a roll, the air that has entered between layers of theintermediate sheet cannot flee and remains as air bubbles, if the frontsurface of the intermediate sheet is a mirror surface; these air bubblesare forced into the intermediate sheet by the tension exerted to thesheet when the sheet is wound up, whereby the intermediate sheet haspyramidal minute projections as defects) does not occur, and also inthat ply adhesion is improved. When the refractive index isdiscontinuous at the layer-layer interface due to fine irregularities ofthe front surface, the front surface may be made into a substantiallysmooth surface to prevent the interface from causing unwanted reflectionof light.

When the surface of the transparent barrier layer is flat, the thicknessof this layer varies according to portions, depending on whether theportions correspond to the openings in the mesh layer or to thenon-opening portions of the mesh layer, and the thickness of theportions that correspond to the openings in the mesh layer is greaterthan that of the other portions by the thickness of the mesh layer.However, from the viewpoint of the barrier function of the transparentbarrier layer, the thickness of those portions of the transparentbarrier layer that correspond to the openings may be the same as that ofthose portions of the transparent barrier layer that correspond to thenon-opening portions (in this case, those portions of the transparentbarrier layer that correspond to the openings form depressions). Inorder for such a transparent barrier layer to have barrier properties,the transparent barrier layer is formed so that its thinnest portion hasa thickness of not less than 1 μm, for example. On the hand, since anexcessively thick transparent barrier layer brings about excessperformance, high cost, and so on, the thickness of the thickest portionof the transparent barrier layer is made not more than 130 μm, forexample.

In order for the transparent barrier layer to have, as desired, a smoothsurface, a matte surface, a mirror surface, or the like, a shaping sheetmay also be used. The shaping sheet is used in the following manner: forexample, a coating liquid for forming the transparent barrier layer isapplied to the mesh layer laminated to the transparent substrate, andthe shaping sheet is placed on the surface of this coating film whilethe coating film is still in the liquid state, whereby the surface ofthe coating film is shaped by the shaping sheet face; after the coatingfilm has solidified into such a degree that its shaped surface canremain in its shape, the shaping sheet is removed. Thus, the transparentbarrier layer can have a surface in the desired shape. Alternatively, ifthe coating film causes plastic deformation when heated even after ithas solidified, shaping may be conducted by placing the shaping sheet onthe coating film even after the coating film has solidified, applyingheat and pressure, and then removing the shaping sheet from the coatingfilm.

Any shaping sheet can be herein used as long as it can shape the surfaceof a coating film, as desired, into a flat surface, for example, and isreleasable from the coating film for the transparent barrier layer, anda properly selected material may be used for such a sheet. In the casewhere an ionizing-radiation-curing resin is used for the transparentbarrier layer and ionizing radiation is applied through the shapingsheet to cure this resin, it is proper to select a material thattransmits ionizing radiation. When ultraviolet light is used as theionizing radiation, it is proper to select a material that transmitsultraviolet light. These materials include sheets of a variety ofresins.

Examples of resins for the above-described resin sheets includepolyester resins such as polyethylene terephthalate, polybutyleneterephthalate, polyethylene naphthalate, ethylene glycol-terephthalicacid-isophthalic acid copolymers, and terephthalic acid-cyclohexanedimethanol-ethylene glycol copolymers; polyamide resins such as nylon 6;polyolefin resins such as polypropylene, polymethyl pentene, and cyclicpolyolefins; imide resins; and polycarbonate. Of these resins, polyesterresins such as polyethylene terephthalate and polyethylene naphthalate,and polyolefin resins such as polypropylene and polynorbornene arepreferred from the viewpoint of flatness, strength, release properties,ultraviolet light transmission properties, heat resistance, and cost.Further, from the viewpoint of mechanical strength, oriented sheets suchas monoaxially or biaxially oriented sheets are preferred. Specifically,biaxially oriented polyethylene terephthalate sheets are most preferred.The thickness of the resin sheet is approximately from 10 to 1000 μm.

To make the shaping face of the shaping sheet not flat or mirror-likebut rough, a resin sheet surface to be used as the shaping face may beembossed, stamped, or chemically etched, or particles may be added tothe resin sheet.

When a shaping sheet composed only of a resin sheet has a shaping facepoor in release properties, a release layer may be formed on the shapingface by the use of a material having release properties, such assilicone.

By properly controlling the release properties of the shaping face ofthe shaping sheet (by decreasing releasability if only the releaseproperties are taken into account), it becomes possible to peel off theshaping sheet together with the transparent barrier layer present on theframe part, while leaving the transparent barrier layer on the mesh partof the mesh layer. Thus, the transparent barrier layer that has beenonce formed on both the frame part and the mesh part can be removedtogether with the shaping sheet only from the frame part to expose theframe part for easy grounding. In controlling the release properties forthis purpose, the wettability of the shaping face, for example, can beused as an index, and it is proper to control the wet tensile strengthto 35-45 mN/m (according to JIS K-6768). To properly control the releaseproperties of the shaping face, the shaping face may also be subjectedto adhesion-promoting treatment such as corona discharge treatment,plasma treatment, ozone treatment, flame treatment, primer coatingtreatment, vacuum deposition, or alkali treatment.

[Functional Layer]

The functional layer 8 is a separate layer that is laminated to thetransparent colored resin layer serving also as an adhesive layer sothat the electromagnetic wave shielding filter additionally performsother functions that the electromagnetic wave shielding filter of theabove-described lamination cannot perform, such as surface protection,enhancement of mechanical strength, improvement in optical properties,and the functions of component parts of a display itself. Theimprovement in optical properties includes the selection of spectra thatcannot be fully attained by the function of the transparent coloredresin layer, and the other optical functions. Examples of the functionallayer for improving optical properties include a variety of filters suchas antireflection (including anti-glaring) filters, infrared absorptionfilters, near infrared absorption filters, neon light absorptionfilters, and complementary color filters. It is possible to employ afunctional layer having any known function that is selected depending onthe use to which the electromagnetic wave shielding filter will be put.How the transparent colored resin layer 4 and the functional layer 8bear their share of the function, improvement in optical properties, orhow these two layers mutually complement each other so as to performthis function, is specifically as follows, for example: a coloring agentthat absorbs infrared rays is incorporated in the transparent coloredresin layer, and a coloring agent that absorbs neon light, in thefunctional layer. When the transparent colored resin layer also servesas an adhesive layer, the functional layer is a separate layer to belaminated by this adhesive layer, and the purpose of laminating theseparate layer is to make the electromagnetic wave shielding filterperform any particular function, or to integrate the separate layerhaving any particular function into the electromagnetic wave shieldingfilter (when the separate layer is, for example, a display frontsubstrate, not the former expression but the latter expression is used;another expression is that a display is provided with an electromagneticwave shielding filter).

Further, the functional layer is prepared as a substantial being,typically in the form of a sheet or plate, and is laminated by thetransparent colored resin layer serving also as an adhesive layer,thereby integrating it into the electromagnetic wave shielding filter.The functional layer can thus be laminated without forming an additionaladhesive layer, so that it is possible to avoid an increase in thenumber of production steps that is brought about by an increase in thenumber of constituent layers, as well as an increase in cost, and soforth. The functional layer may also be a coating film formed bycoating, printing, or the like. In this case, the transparent coloredresin layer serves also as an adhesive layer that makes up the adhesiveproperties of the coating film when the coating film itself is poor inadhesive properties.

Such a functional layer may be a conventional substantial being such asan optical filter or a front substrate of a display itself.Alternatively, the functional layer may be formed by the use of a paintor ink useful for forming a coating film that serves as an opticalfilter. Of these functional layers, a filter in the form of a sheet orplate is typical.

For the above-described optical filter can be used conventional ones,and commercially available filters (sheets, plates) may be herein used.These filters will now be described in more detail.

FIG. 5, a sectional view, illustrates an electromagnetic wave shieldingfilter 10 having the following structure: The functional layer 8 is alaminate of a functioning layer 8A that performs the main function ofthe functional layer serving as a hard coat layer, a coloring filterlayer, or the like, and a transparent substrate 8B that reinforces andsupports the functioning layer: The functional layer 8 is laminated tothe surface of the transparent barrier layer 5 through the transparentcolored resin layer 4 serving also as an adhesive layer, with thetransparent substrate 8B facing to the transparent barrier layer 5,thereby integrating the functional layer 8 into the electromagnetic waveshielding filter 10 so that the functioning layer 8A is the outermostsurface layer. Although the functional layer may be a single layer(e.g., a surface protective sheet made of a single-layer resin film),FIG. 5 illustrates the case where the functional layer is composedroughly of two layers, the functioning layer 8A and the transparentsubstrate 8B that supports the functioning layer 8A. Although each ofthe functioning layer 8A and the transparent substrate 8B may becomposed of a single layer or of multiple layers, this figureillustrates the functional layer as being composed roughly of thefunctioning layer and the transparent substrate. The functional layermay also be composed of functioning layers and transparent substratesthat are laminated alternately. Moreover, the functional layer may alsobe laminated to the transparent colored resin layer, with thefunctioning layer side facing to the transparent colored resin layer.

The functioning layer 8A may be of any type. For example, the functionallayer 8 is formed as a neon light absorption filter by incorporating aneon light absorber to the functioning layer 8A, while the transparentcolored resin layer 4 to which the functional layer 8 will be laminated,with its transparent substrate 8B facing to the transparent coloredresin layer 4, is formed, by adding a near infrared absorber, as a nearinfrared absorption filter layer serving also as an adhesive layeruseful in laminating the functional layer 8. Of course, the aboveconstruction is merely one specific example of combinations of thefunction of the functioning layer 8A and that of the transparent coloredresin layer 4.

The hard coat layer (HC layer) may be a coating film of anionizing-radiation-curing resin containing a polyfunctional(meth)acrylate prepolymer such as polyester (meth)acrylate, urethane(meth)acrylate, or epoxy (meth)acrylate, preferably a polyfunctional(meth)acrylate monomer with three or more functionality, such astrimethylol propane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, or dipentaerythritol hexa(meth)acrylate.

The antireflection layer (abbreviated to AR layer) includes severalforms of antireflection layers, such as the dielectric multi-layerinterference form in which low-refractive-index layers andhigh-refractive-index layers are alternately laminated, with alow-refractive-index layer on the outermost side. Either a dry methodsuch as vacuum deposition or sputtering, or a wet method such as coatingmay be employed to form the above layers. Silicon oxides, magnesiumfluoride, fluoroplastics, and the like may be used for thelow-refractive-index layers, and titanium oxide, zinc sulfide, zirconiumoxide, niobium oxide, and the like, for the high-refractive-indexlayers.

Another form of the antireflection layer useful herein is one that makesuse of the diffusion of light that is caused by fine surfaceirregularities or by an interface, existing inside the layer, betweentwo phases having different refractive indices (commonly called ananti-glaring layer, which is abbreviated to AG layer). Such anantireflection layer may be a coating film formed by using a resinbinder to which inorganic filler such as silica has been added, or alayer having, on its surface, fine irregularities that scatterextraneous light, formed by using a shaping sheet, a shaping plate, orthe like. Curable acrylic resins, as well as ionizing-radiation-curingresins useful for the above-described hard coat layer, are favorable forthe resin binder because the antireflection layer is required to havesurface strength high enough for a surface layer.

Further, to form a near infrared absorption filter, an infraredabsorption filter, a neon light cutting filter, a color tonecompensation filter, or the like as the functional layer, a mixture of amatrix such as a resin and a coloring agent may be used, where thecoloring agent is one of the coloring agents previously mentioned inconnection with the transparent colored resin layer, selected dependingon how the functional layer and the transparent colored resin layer beartheir share of the desired function, or on how these two layers mutuallycomplement each other so as to perform the desired function.

The functional layer may be laminated not only to the transparentcolored resin layer by making use of the adhesive properties of thetransparent colored resin layer, but also to the back surface of thetransparent substrate by a proper adhesive agent.

EXAMPLES

The present invention will now be explained more specifically by way ofExamples and Comparative Example.

Example 1

The electromagnetic wave shielding filter 10 shown in FIG. 6(A) wasproduced in the following manner. Continuous belt-like electrolyticcopper foil with a thickness of 10 μm, having on one surface ablackening layer 7 made from copper-cobalt particles, was firstlyprepared as the metal foil to be made into the electrically conductivelayer 2. A non-colored, transparent, biaxially oriented, polyethyleneterephthalate film in the form of a continuous belt with a thickness of100 μm was prepared as the transparent substrate 1.

After plating with zinc, both surfaces of the above-described copperfoil were subjected to conventional chromate treatment by immersing thecopper foil in a chromate treatment light, thereby forming anticorrosivelayers 6 on the surface and the back surface of the copper foil.Subsequently, this copper foil was dry-laminated to the transparentsubstrate, with the blackening layer side facing to the transparentsubstrate, by a urethane adhesive made of a transparent two-pack curableurethane resin consisting of 12 parts by weight of polyesterpolyurethane polyol with a mean molecular weight of 30,000 and 1 part byweight of xylene diisocyanate prepolymer. This laminate was then aged at50° C. for 3 days, thereby obtaining a continuous belt-like,copper-foil-laminated sheet having a 7-μm thick transparent adhesivelayer 9 between the copper foil (anticorrosive layer) and thetransparent substrate.

Thereafter, the copper foil (the electrically conductive layer, theblackening layer, and the anticorrosive layer) contained in theabove-described copper-foil-laminated sheet was photolithographicallyetched. Thus, there was obtained a mesh-laminated sheet containing, onthe transparent substrate 1, a mesh layer 3 consisting of theanticorrosive layer 6, the electrically conductive layer 2, and theblackening layer 7.

Specifically, by using the existing production line for shadow masks forcolor TVs, the copper-foil-laminated sheet in the form of a continuousbelt was subjected to a series of the steps of from masking to etching.First, a resist for etching was applied to the entire surface of theelectrically conductive layer in the copper-foil-laminated sheet. Thissheet was subjected to contact exposure to light using a patterningplate for the desired mesh pattern, and was then subjected todevelopment, film hardening treatment, and baking. Thereafter, by usinga ferric chloride solution, the copper foil was etched together with theblackening layer, thereby making openings in the copper foil to form amesh. The copper foil was then successively subjected to washing withwater, resist stripping, cleaning, and drying. As for the mesh layer,the shape of each opening was a regular square; the line width of theline parts, non-opening portions, was 10 μm; the distance between thelines (line pitch) was 300 μm; and the bias angle that is defined as aminor angle with the longer side of the rectangular mesh part 3A (seeFIG. 2) was 49 degrees. Etching was conducted in such a way that, whenthe continuous, belt-like sheet is cut into rectangular sheets in thedesired size, non-etched portions that form a 15-mm wide frame parthaving no openings surround the four sides of each sheet.

Subsequently, the above-described mesh-laminated sheet that had beenonce rolled up was unrolled, and a coating liquid made from anionizing-radiation-curing resin composition was intermittently applied,by intermittent die coating, to the mesh layer face of themesh-laminated sheet in an amount of 25 g/m² on dry basis, provided thatthe area coated with the coating liquid was the entire mesh part and a2.5-mm wide inner peripheral area of the frame part, stretchingadjacently to and around the mesh part, thereby forming the transparentbarrier layer 5 on the mesh layer face. The coating liquid was anionizing-radiation-curing resin composition prepared by adding 0.3% byweight of a photopolymerization initiator [Irgacure (trademark) 184manufactured by Ciba Specialty Chemicals K.K., Japan] to a 1:1 (weightbasis) mixture of urethane acrylate oligomer and phenoxyethyl acrylateand diluting this mixture with an organic solvent (a 1:1 (weight basis)solvent mixture of methyl ethyl ketone and toluene).

After applying the coating liquid, the coating film formed was dried toevaporate the solvent, and a shaping sheet, which was a commerciallyavailable, 50-μm thick, biaxially oriented polyethylene terephthalatefilm in a continuous, belt-like form, was placed on this coating film,with its non-adhesion-promoted surface facing to the coating film. Afterapplying ultraviolet light (using a D bulb manufactured by Fusion UVSystems Co., Ltd., Japan) through the shaping sheet to cure the coatingfilm, only the shaping sheet was peeled off, thereby forming atransparent barrier layer 5 in a non-sticky solid state, having a flatsurface. Thus, a sheet to be processed was obtained.

Subsequently, a transparent colored resin layer in the form of a coloredpressure-sensitive adhesive sheet with separators on both sides wasprepared, in order to form, on the flat front surface of the transparentbarrier layer, the transparent colored resin layer 4 serving also as anadhesive layer (pressure-sensitive adhesive layer) useful in laminatinga functional layer. Namely, to the releasing face of a continuous,belt-like separator with a polyethylene terephthalate film substrate, acolored, acrylic resin pressure-sensitive adhesive (binder) to which acyanine dye (TY-167 manufactured by ASAHI DENKA KOGYO K.K., Japan), aneon light absorber, had been added in such a proportion that the dyeconcentration of the transparent colored resin layer would be 0.00325g/m² was applied to form a coating film with a uniform thickness (in anamount of approximately 25 g/m² when calculated in terms of solidmatter). After evaporating the solvent, a similar separator was attachedto the sticky surface, thereby obtaining a continuous belt-like,colored, pressure-sensitive adhesive sheet with the separators on bothsides. This continuous belt-like, colored, pressure-sensitive adhesivesheet was laminated, while removing the separator from one side of thissheet, to a non-colored, transparent, biaxially oriented, 100-μm thickpolyethylene terephthalate film in the form of a continuous belt, to beused as a functional layer 8 useful for surface protection, whereby acontinuous, belt-like protective sheet with the colored,pressure-sensitive adhesive layer was obtained. The continuousprotective sheet with the colored, pressure-sensitive adhesive layer wasslit and cut into sheets in such a desired size that the frame partaround the four sides of the filter was exposed, thereby obtainingprotective sheets with the colored, pressure-sensitive adhesive layer.These protective sheets were intermittently laminated, while removingthe separators from the protective sheets, to the above-describedcontinuous belt-like sheet to be processed, in such a manner that theframe part around the four sides of the mesh layer was exposed (theinner peripheral area of the frame part was slightly covered), whereby alaminate shown in FIG. 6(A) was obtained. By cutting this laminate intothe desired size, an electromagnetic wave shielding filter 10 shown inFIG. 6(A), in sheet form, was finally obtained.

The lamination of the electromagnetic wave shielding filter 10 shown inFIG. 6(A) is the transparent substrate 1/the transparent adhesive layer9/the mesh layer 3 (the anticorrosive layer 6/the blackening layer 7/theelectrically conductive layer 2/the anticorrosive layer 6)/thetransparent barrier layer 5/the transparent colored resin layer 4/thefunctional layer 8, where the transparent substrate 1 side is theobserver side. The symbol “/” herein denotes that two layers writtenbefore and after this symbol are integrally laminated to each other, andthis shall apply hereinafter.

Example 2 Formation of Blackening Layer on the Other Side ofElectrically Conductive Layer

An electromagnetic wave shielding filter 10 comprising a blackeninglayer 7 formed, as shown in FIG. 6(B), on the electrically conductivelayer 2 face on the transparent colored resin layer 4 side, opposite tothe side on which the blackening layer 7 was formed in Example 1, wasproduced in the following manner.

An electromagnetic wave shielding filter 10 shown in FIG. 6(B) wasproduced in the same manner as in Example 1, except that the copper foilcovered with the anticorrosive layer was laminated to the transparentsubstrate, with the non-blackened surface of the copper foil facing tothe transparent substrate.

The lamination of the electromagnetic wave shielding filter 10 shown inFIG. 6(B) is the transparent substrate 1/the transparent adhesive layer9/the mesh layer 3 (the anticorrosive layer 6/the electricallyconductive layer 2/the blackening layer 7/the anticorrosive layer 6)/thetransparent barrier layer 5/the transparent colored resin layer 4/thefunctional layer 8, where the transparent colored resin layer 4 side isthe observer side.

Example 3 Formation of Blackening Layer on Three Faces of ElectricallyConductive Layer

An electromagnetic wave shielding filter 10 comprising a blackeninglayer 7 formed on the surface and the both side faces of an electricallyconductive layer 2, as shown in FIG. 6(C), was produced in the followingmanner.

In the same manner as in Example 1, a copper-foil-laminated sheet wasprepared by using, as the metal foil to be made into the electricallyconductive layer 2, electrolytic copper foil that had not been subjectedto blackening treatment, and was etched, thereby obtaining a laminatesheet having an electrically conductive layer in the form of a mesh.Subsequently, a blackening layer 7 also having the function ofpreventing corrosion was formed on three faces, that is, the surface(the face on the side opposite to the transparent substrate side) of theelectrically conductive layer, and the both side faces of each openingin the mesh. Specifically, the laminate sheet containing, on thetransparent substrate, the electrically conductive layer in the form ofa mesh was immersed in a plating bath for blackening treatment, amixture of an aqueous nickel ammonium sulfate solution, an aqueous zincsulfate solution, and an aqueous sodium thiocyanate solution, to conductelectrolytic plating, using a nickel plate as the anode, therebyconducting blackening treatment to form a nickel-zinc-alloy-madeblackening layer 7 on the above-described three faces, that is, theentire exposed surface of the electrically conductive layer. Thus, therewas obtained a mesh-laminated sheet having, on the transparent substrate1, the mesh layer 3 consisting of the electrically conductive layer 2and the blackening layer 7. To this mesh-laminated sheet, a transparentbarrier layer, a transparent colored resin layer, and a functional layerwere successively laminated in the same manner as in Example 1, exceptthat the anticorrosive layer was not formed, whereby an electromagneticwave shielding filter shown in FIG. 6(C) was obtained.

The lamination of the electromagnetic wave shielding filter 10 shown inFIG. 6(C) is the transparent substrate 1/the transparent adhesive layer9/the mesh layer 3 (the electrically conductive layer 2/the blackeninglayer 7 on the surface and the both side faces)/the transparent barrierlayer 5/the transparent colored resin layer 4/the functional layer 8,where the transparent colored resin layer 4 side is the observer side.

Example 4 Direct Formation of Electrically Conductive Layer onTransparent Substrate

An electromagnetic wave shielding filter 10 shown in FIG. 6(D),comprising an electrically conductive layer 2 laminated directly to atransparent substrate 1 without using a transparent adhesive layer, anda blackening layer 7 formed on the three faces of the electricallyconductive layer 2, that is, the surface and the both side faces of theelectrically conductive layer 2, was produced in the following manner.

A non-colored, transparent, 100-μm thick, biaxially orientedpolyethylene terephthalate film in the form of a continuous belt wasprepared as the transparent substrate 1. By conducting vacuumdeposition, a copper layer with a thickness of 0.5 μm (a part of theelectrically conductive layer) was formed, as a conductive treatmentlayer, on one surface of the above transparent substrate. A copper layerwith a thickness of 10 μm (the remaining part of the electricallyconductive layer) was formed on the conductive treatment layer face byelectrolytic plating. Thus, there was obtained a copper-laminated sheetcontaining the electrically conductive layer 2 consisting of the twocopper layers, formed directly on the transparent substrate.

By repeating the same subsequent steps as in Example 3, anelectromagnetic wave shielding filter shown in FIG. 6(D) was obtained.

The lamination of the electromagnetic wave shielding filter 10 shown inFIG. 6(D) is the transparent substrate 1/the mesh layer 3 (theelectrically conductive layer 2/the blackening layer 7 on the surfaceand the both side faces)/the transparent barrier layer 5/the transparentcolored resin layer 4/the functional layer 8, where the transparentcolored resin layer 4 side is the observer side.

Comparative Example 1

An electromagnetic wave shielding filter 20 having the structure shownin FIG. 7(C) was produced in the same manner as in Example 1, exceptthat the transparent barrier layer was not formed. Specifically, anelectromagnetic wave shielding filter 20 shown in FIG. 7(C) was producedin the same manner as in Example 1, except that the protective sheets inthe desired size, covered with the colored, pressure-sensitive adhesivelayer, were laminated to the continuous belt-like, mesh-laminated sheetin the state of being not provided with the transparent barrier layer,and that, after cutting this laminate into final sheets in the desiredsize, the air bubbles incorporated due to the difference in levelproduced by the mesh layer and remaining even after the laminating step,were removed in an autoclave at 1 MPa (10 atom) and 80° C. over 1 hour.

The lamination of the electromagnetic wave shielding filter 20 shown inFIG. 7(C) is the transparent substrate 1/the transparent adhesive layer9/the mesh layer 3 (the anticorrosive layer 6/the blackening layer 7/theelectrically conductive layer 2/the anticorrosive layer 6) thetransparent colored resin layer 4/the functional layer 8, where thetransparent substrate 1 side is the observer side.

[Performance Assessment]

Performance assessment was carried out in the following manner: beforeand after heating at 80° C. for 1,000 hours, the color tone of each oneof the electromagnetic wave shielding filters of Examples andComparative Example (the whole electromagnetic wave shielding filterincluding not only the transparent colored resin layer but also theother constituent layers) was determined by a spectrocolorimeter(CM-3600d manufactured by KONICAMINOLTA SENSING CO., LTD., Japan) inorder to obtain the color difference ΔE*Lab, which is defined asΔE*Lab={(ΔL*)²+(Δa*)²+(Δb*)²}^(0.25) in the L*a*b* color system providedby CIE (International Commission on Illumination, 1976). The measurementwas made by using standard light D₆₅ at a viewing angle of 2° intransmission mode.

The results are as shown in Table 1. The color difference obtained fromthe electromagnetic wave shielding filters of Examples are 2.0 or less;while the color difference obtained from the electromagnetic waveshielding filter of Comparative Example is more than 4 that is in excessof two times the color differences obtained from the electromagneticwave shielding filters of Examples. Thus, the change in color that theelectromagnetic wave shielding filters of Examples had undergone waslittle, and it was thus confirmed that these filters had been improved.

TABLE 1 Results of Performance Assessment Color Difference ΔE*Lab(before and after heating at 80° for 1000 hrs.) Example 1 1.9 Example 21.8 Example 3 2.0 Example 4 1.9 Comp. Ex. 1 4.1

1. An electromagnetic wave shielding filter comprising: a transparentsubstrate, a transparent adhesive layer made from a urethane adhesive,formed on the transparent substrate, a mesh layer in the form of a mesh,containing at least an electrically conductive layer made from a metal,formed on the transparent adhesive layer, and a transparent coloredresin layer containing a coloring agent and an adhesive, formed on themesh layer, a transparent barrier layer for separating the mesh layerand the transparent colored resin layer from each other, made from anon-urethane, non-adhesive solid resin, being present between the meshlayer and the transparent colored resin layer.
 2. The electromagneticwave shielding filter according to claim 1, wherein the mesh layercontains an anticorrosive layer formed at least on one side of theelectrically conductive layer.
 3. The electromagnetic wave shieldingfilter according to claim 1, wherein the mesh layer contains ablackening layer formed at least on one side of the electricallyconductive layer.
 4. The electromagnetic wave shielding filter accordingto claim 1, wherein the mesh layer contains a blackening layer, theelectrically conductive layer, and an anticorrosive layer that aresituated in this order, with the blackening layer on the transparentsubstrate side.
 5. The electromagnetic wave shielding filter accordingto claim 1, wherein the mesh layer contains the electrically conductivelayer, a blackening layer, and an anticorrosive layer that are situatedin this order, with the electrically conductive layer on the transparentsubstrate side.
 6. The electromagnetic wave shielding filter accordingto claim 1, wherein the mesh layer contains a first anticorrosive layer,a blackening layer, the electrically conductive layer, a blackeninglayer, and a second anticorrosive layer that are situated in this order,with the first anticorrosive layer on the transparent substrate side. 7.The electromagnetic wave shielding filter according to claim 1, whereinthe mesh layer contains a first anticorrosive layer, the electricallyconductive layer, a blackening layer, and a second anticorrosive layerthat are situated in this order, with the first anticorrosive layer onthe transparent substrate side.
 8. The electromagnetic wave shieldingfilter according to claim 1, wherein the mesh layer contains theelectrically conductive layer, and a blackening layer that covers a faceof the electrically conductive layer on the side opposite to thetransparent substrate side and the side faces of the electricallyconductive layer.
 9. The electromagnetic wave shielding filter accordingto claim 1, wherein the transparent colored resin layer functions as anadhesive layer, and a functional layer is laminated to the transparentcolored resin layer.
 10. The electromagnetic wave shielding filteraccording to claim 1, further comprising: a transparent adhesive layerbetween the transparent substrate and the mesh layer.
 11. Theelectromagnetic wave shielding filter according to claim 1, wherein themesh layer contains a blackening layer formed, either directly orthrough an anticorrosive layer, on one or more faces selected from aface of the electrically conductive layer on the transparent substrateside, a face of the electrically conductive layer on the side oppositeto the transparent substrate side, and the side faces of theelectrically conductive layer.